For starters, you can check in with the California-based Snell Foundation, one of the best resources in the country when it comes to helmet safety standards. The non-profit was established in 1957 in honor of Peter Snell, a race car driver who died of a head injury after he rolled his car while wearing a helmet made from compressed cardboard and leather.

Most skiing, snowboarding, climbing, and cycling helmets are made with an EPS (or expanded polystyrene) liner. "EPS is essentially plastic beads with air bubbles—packed together very tightly—and that density [determines] how the air pockets function," Snell Foundation Director of Education Hong Zhang said.

Those air bubbles crunch down during impact to cushion your head, meaning you have to replace an EPS helmet after just one crash. "Even if your head hits just a little bit—like a fall from one or two feet—the inside liner is compromised," Zhang said.

POC Sports, the company that made the U.S. Ski Team Olympic helmets, recently developed an EPP (expanded polypropylene) liner. The company claims this material retains its shape after a crash and can survive multiple impacts. "No need to replace after hits unless the hits are very severe or repetitive in high numbers. Replace after two to five seasons for maximum performance (just like with ski boots, skis, etc)," Oscar Huss, head of product development for POC Sports, wrote in an email.

Even if you never crash in a helmet, the Snell Foundation suggests replacing the lid after about five years. "Sweat, hair product, and cleaning solution break down EPS," Zhang said. The interior padding also breaks down over time, which will affect how the helmet fits. This general wear and tear can make the helmet a whole size larger, says Zhang.

While it might seem exorbitant to replace a helmet after every crash or every two to five seasons, remember a new helmet is a lot less expensive than a trip to the emergency room.

What You Need to Know:

An EPS helmet is good for only one crash.

An EPP helmet can withstand multiple impacts, unless the hits are very severe.

Don’t use any helmet for more than five seasons, even if you’ve never crashed in it.